The present invention relates generally to an improved system for delivery of ultra-high pressure water from a pump/intensifier to the nozzle of a waterjet cutting system, and more particularly to such a system which provides for a continuous flow from the pump/intensifier through the entire system and with nozzle discharge being at a pre-selected working pressure of either an ultra-high or a high pressure range. The arrangement of the present invention facilitates utilization of waterjet cutting systems for piercing operations on brittle or hard materials, as well as utilization of these systems on such materials without requiring cut-initiation from an outside edge of the workpiece. The features of the present invention will be discussed in detail hereinbelow.
Waterjet cutting systems are typically used for forming or cutting irregular or unusual patterns in dense and/or hard materials. Frequently, entrained abrasive is added to the discharge so as to provide a greater cutting force with the focused discharge stream of ultra-high pressure water from the nozzle. These systems are adapted for use in cutting or shaping brittle materials including metals, plastics and glass, including hardened glass as well as stone objects consisting of marble, granite or the like. Fragile materials are also uniquely suited for some types of ultra-high pressure waterjet cutting systems.
By definition, ultra-high pressure water systems typically utilize an operating pressure of at least 55,000 psi. In certain applications, pressures as high as 75,000 psi have been found useful as well.
In the operation of waterjet cutting systems, all components are subject to mechanical wear and require periodic maintenance and service. In a typical operational system, one component requiring an unusual amount of attention is the pump/intensifier. Maintenance problems are occasioned in significant part by the number of start-up cycles to which the pump/intensifier is subjected, rather than simply the time duration of operation. When subjected to less frequent start-ups, the overall life of a pump/intensifier between overhauls can be extended. The present invention facilitates operational cycles of longer duration, with the pump operating continuously under substantially the same high pressure conditions during the duration of these operational cycles.
In accordance with current practice, whenever it is desirable to change operational parameters such as cut location, or simply the introduction of fresh workpieces to the system, the operator typically de-energizes the pump/intensifier. By contrast, and in accordance with the present invention, the operator actuates a selector valve which is interposed between the pump/intensifier and the cutting nozzle, with this being a "T" valve and creating a normally open, continuously running lower working pressure bypass flow between the pump/intensifier and the cutting head. The bypass includes a pressure reducer in which the pressure of water passing through the bypass is dropped from the ultra-high level to a substantially lower but nevertheless working pressure level. Stated another way, in the line coupling the pump/intensifier to the cutting head a pressure reducer/bypass is interposed which is maintained in a normally open position during all periods of operation of the pump/intensifier.
The dual pressure selector valve arrangement enables constant operation of the pump/intensifier. Accordingly, the present invention employs a nozzle assembly and selector valve so as to deliver a constant stream of water entrained abrasive (if desired) to the surface of a workpiece at either of two significantly different working pressures. The system includes a cutting head capable of delivering water at a first ultra-high pressure in excess of about 55,000 psi, and also at a second somewhat reduced working pressures such as in the area of between about 5,000 and 55,000 psi. This arrangement makes it possible for the pump/intensifier to maintain continuous operation at the ultra-high pressure level for heavy duty cutting operations, without necessarily having to occasionally vary its operational parameters between ultra-high working pressure and a somewhat reduced but effective working pressure.
The ultra-high working pressure is utilized for conventional cutting applications, with the lower working pressure being utilized for initiating cuts or for piercing workpieces. This pressure reduction feature is particularly helpful when the workpiece consists of a brittle material such as glass, acrylics, some laminates, brittle metals and the like. The higher pressure working streams are prone to fracture the edges and/or the surfaces of the workpiece. In other words, the workpiece is better able to withstand forces from ultra-high working pressures as the cutting zone is ultimately moved inwardly from the peripheral edge, or when a piercing operation is completed. Since, the workpieces are better able to withstand forces from ultra-high working pressures and forces created from exposure to ultra-high working pressures once the workpiece has been completely pierced.
In accordance with the present invention, a selector valve arrangement is provided having an internal "T" arrangement in the head assembly. High pressure water enters the valve and passes into a three-way chamber with flow being controlled by a needle valve. In its closed position, the needle valve causes the water to pass through the channel leading to a series of cylindrical members with eccentric bores formed therein to create a drop in pressure, while at the same time permitting a modest flow rate to continue. This flow rate and operating pressure represent the lower of the two working pressures being delivered through the system. When ultra-high pressure is needed the needle valve is opened, whereupon flow of ultra-high pressure water passes through the main passageway and directly to the cutting head. The lower pressure line remains open during the entire operation, and in effect creates a parallel flow pattern without disruption of the coherent nature of the high pressure flow.
Therefore, it is the primary object of the present invention to provide an improved waterjet cutting system which employs a nozzle assembly provided with a means for delivering a stream of water or water with entrained abrasive onto a workpiece at two significantly different working pressures, with the pump/intensifier operation being uninterrupted.
It is a further object of the present invention to provide an improved waterjet cutting system which permits continuous operation of a pump/intensifier while delivering water entrained abrasive to a workpiece at either one of two selected working pressures, with one of the working pressures being an ultra-high pressure, and with the other being at a reduced but yet effective working or cutting pressure.
It is yet a further object of the present invention to provide a waterjet cutting system which permits the pump/intensifier to maintain operation continuously while cutting operations are undertaken at either of two selected working pressures.
It is still a further object of the present invention to provide an improved waterjet cutting system designed to initiate cuts and/or piercing of workpieces through the utilization of a pressure reduction feature which permits the discharge of water entrained abrasive at working pressures significantly less than ultra-high working pressures employed for normal cutting.
Other and further objects of the present invention will become apparent to those skilled in the art upon a study of the following specification, appended claims and accompanying drawings.